The present invention relates to photodiode devices exhibiting photoconductive gain enhancement.
Photodiodes are one of the most basic building blocks of photonic systems, and the physics of p-i-n diodes is an area considered by many to be well understood. Conventional treatment of a pi-n diode assumes a maximum photoconductive gain of unity, g=1. This assumption has proven so reliable for bulk photodiodes that it has become accepted as a fundamental property of photodiodes, although the mechanisms preventing greater than unity photoconductive gains have not been well described in the literature. More recently, p-i-n photodiodes have been designed with heterojunction structures (such as multiple quantum well structures) in the intrinsic region, and to date these devices have been modeled using the same assumption of unity photoconductive gain (for example see M. K. Chin and W. S. C. Chang, xe2x80x9cInGaAs/InAIAs Quantum-Well Electroabsorption Waveguide Modulators With Large-Core Waveguide Structure: Design And Characterizationxe2x80x9d, Appl. Opt., 34:1544-1553, 1995; A. M. Fox, D. A. B. Miller, G. Livescu, J. E. Cunningham, and W. Y. Jan, xe2x80x9cQuantum Well Carrier Sweep Out: Relation To Electroabsorption And Exciton Saturationxe2x80x9d, IEEE J. Quantum Electron., 27:2281-2295, 1991).
The ability to produce photodiodes with controlled photoconductive gain would be of great benefit for use in photodetector devices and the like. For example, any application requiring detection of very low light intensity levels would benefit significantly with the use of photodiodes having photoconductive gain. Therefore, it would be advantageous to provide semiconductor photodiodes exhibiting photoconductive gain.
It is an object of the present invention to provide photodiode devices exhibiting photoconductive gain.
The inventor has demonstrated that photodiodes may exhibit photoconductive gain under certain conditions, and that these gains may be described to first order by a simple extension of photoconductive gain theory. In the present application there is introduced the basic principles of photoconductive gain in p-i-n diodes, and there is described several approaches to designing photodiodes with photoconductive gain.
In one aspect of the invention there is provided a photodiode with photoconductive gain, comprising:
a semiconductor including at least one p-type region, at least one n-type region, and electrical contacts attached to said n-type region and to said p-type region, whereby illuminating said semiconductor generates electron-hole pairs in at least one depletion region formed at a p-n junction; and
means for enhancing an electron-hole pair generation rate in at least a portion of said semiconductor outside said at least one depletion region,
In this aspect of the invention the means for enhancing an electron-hole pair generation rate may comprise the at least a portion of the semiconductor including an effective semiconductor material having a minority carrier lifetime shorter than or on an order of a difference between the average times for an electron and a hole photogenerated within a specific depletion region to escape the specific depletion region.
In this aspect of the invention the means for enhancing an electron-hole pair generation rate in at least a portion of the semiconductor outside the at least one depletion region may be by optical stimulation of the at least a portion of the semiconductor.
In another aspect of the invention there is provided a photodiode with photoconductive gain, comprising:
a semiconductor including at least one p-type region, at least one n-type region, at least one intrinsic region, and electrical contacts attached to said n-type region and to said p-type region, whereby illuminating said semiconductor generates electron-hole pairs in at least one depletion region formed at a p-n junction and/or at an intrinsic region; and
means for enhancing an electron-hole pair generation rate in at least a portion of said semiconductor outside said at least one depletion region.